This research is aimed at identifying the causal status of the genetic determinants and correlates of rats that have been selectively bred for good and poor avoidance learning. It will also examine whether or not there are genetic differences in ACTH release or in the synthesis of corticosterone using HPLC methods to separate the steroids. Implantable osmostic pumps will be used to manipulate the prenatal endocrine environment of animals of the two strains to determine whether the steroids mediate the expression of the gene(s) that control(s) the avoidance phenotypes and their correlates. Limbic structures will also be examined to identify differences in morphometry and in neurotransmitters, again using HPLC methods to separate the biogenic amines. In addition, three behavioral paradigms that are accepted as sensitive to anxiety will be used to study the effects of anxiolytic drugs that bind to the GABA-BZP receptor systems of the brain.